This invention relates to a resonator primarily for air induction systems or exhaust systems, and more particularly, the invention relates to a quarter wave tube having a variable length and volume.
Internal combustion engines produce undesirable induction noise which adversely affects the output torque and volumetric efficiency of the engine. The induction noise produced by the engine depends on the particular engine configuration and is affected by such factors as the number of cylinders, the volume and shape of the intake manifold plenum and intake runners, and other induction system parameters. The induction noise is caused by a pressure wave that travels from the combustion chamber towards the inlet of the air induction system. The induction noise may be reduced by producing a wave traveling in the direction of the combustion chamber 180 degrees out of phase of the noise wave. To this end, noise attenuation devices such as quarter wave tubes have been developed.
A prior art quarter wave tube is shown in FIG. 1. The induction system includes a body 10 such as a zip tube which defines a passageway 12. The quarter wave tube 14 is in fluid communication with the passageway 12. A quarter wave tube produces a noise canceling wave of a frequency that is one quarter the length of the quarter wave tube 14. Typically, quarter wave tubes are of a fixed length and therefore are designed for a particular frequency. Air induction noise is typically concentrated about several different engine orders or operating conditions of the engine. Additionally, the noise frequency changes as the engine speed changes. Since space is limited under the hood of the vehicle, quarter wave tubes are only provided for the most undesirable noise frequencies and the other noise frequencies are not attenuated. Therefore, what is needed is a quarter wave tube or a group of quarter wave tubes that can change to accommodate the changing noise frequencies during engine operation so that a greater amount of air induction noise may be attenuated.
The present invention provides a resonator for an air system that includes a body defining a passageway. A wall is disposed within the chamber and the wall and the chamber are movable relative to one another to define a length and a volume of the cavity. The length and the volume of the cavity defines a noise attenuating frequency. By moving the wall and chamber relative to one another the noise attenuating frequency may be changed as the noise frequency changes during the engine operation. The drive mechanism moves the wall and the chamber relative to one another to change the noise attenuating frequency. The chamber may be a branched-type resonator or an inline-type resonator. Accordingly, the above described invention provides a resonator that may be adjusted during engine operation to attenuate noise over a variety frequencies.